1. Field of the Invention
The present invention relates to a III-V group compound semiconductor light emitting device and to a manufacturing method thereof, and more specifically, to a III-V group compound semiconductor light emitting device allowing highly efficient extraction of light to the outside and to a manufacturing method thereof.
2. Description of the Background Art
Conventionally, a sapphire substrate is mainly used for a III-group compound semiconductor light emitting device, and nitride semiconductor light emitting devices including sapphire substrates have been commercially available. Here, as a sapphire substrate is an insulator, both p-side and n-side electrodes are arranged on a plurality of III-group nitride semiconductor layers formed on one main surface of the substrate. (See, for example, Japanese Patent Laying-Open No. 2003-163373 (hereinafter referred to as Reference 1) and Japanese Patent Laying-Open No. 2002-026392 (hereinafter referred to as Reference 2)).
Referring to FIG. 6, the III-group nitride compound semiconductor light emitting device disclosed in Reference 1 has, on a sapphire substrate 601, a buffer layer 602, a first reflection layer 606, an n-type semiconductor layer 603, a light generating layer 604, a p-type semiconductor layer 605, a second reflection layer 607 and a p-side electrode 608 stacked in this order. On a partially exposed portion of n-type semiconductor layer 603, an n-side electrode 609 is formed. In the example of FIG. 6, the second reflection layer 607 also serves as p-side electrode 608.
Specifically, in the light emitting device shown in FIG. 6, light emitted from light generating layer 604 is resonated between the first and second reflection layers 606 and 607, and thereafter emitted efficiently to the outside through sapphire substrate 601, whereby optical output of the light emitting device is improved. For this purpose, the first reflection layer 606 is adapted to have lower reflectance than the second reflection layer 607.
In the semiconductor light emitting device disclosed in Reference 2 also, an electrode of high reflectance is similarly provided on the side of p-type semiconductor layer, so that the light from the light generating layer is reflected toward the sapphire substrate, and hence efficiency of taking light to the outside is improved.
In the light emitting devices disclosed in References 1 and 2, the n-side and p-side electrodes are provided on a stacked body of semiconductor layers formed on one main surface of the substrate. The light emitting device is connected to the outside by a metal wire. Here, pad electrodes formed on the p-side electrode 608 and n-side electrode 609 of the light emitting device put obstruction in taking out the light from the light generating layer. Further, as n-type semiconductor layer 603 is exposed, it becomes necessary to form n-side electrode 609 by removing a part of light generating layer 604 of the light emitting device, resulting in a non-emitting portion in the light emitting device. As the light generating area of an active layer becomes smaller than the chip area in the direction of the plane of the substrate, there is a loss in light extraction from the light emitting device per chip area.
Further, in light emitting devices disclosed in References 1 and 2, a metal layer having high reflectance (reflection layer) is provided on a p-type GaN layer, and therefore, the light from the active layer is reflected by the reflecting layer and emitted through the substrate, dependent on the device structure. It is noted, however, that as metals are used for the reflecting layer and the layer in contact therewith, atoms in respective layers diffuse to each other. Therefore, different types of atoms undesirably enter the reflection layer from the metal layer in contact with the reflection layer, lowering the reflectance of the reflection layer.